I’ve seen photos like this before, and I always thought that the men were imitating the painting of "Napoleon in his Study." The emperor, I’d heard, clutched his torso because of a stomach ulcer.

But it seems odd (at least to me) that when you have what would’ve been a rare opportunity to capture your likeness for posterity, you'd decide to undo a couple of coat buttons and stick your hand inside the opening.

When I looked into it, I learned that men who posed this way weren’t necessarily imitating Napoleon, and that he wasn’t sticking his hand in his coat because of an ulcer (though he did have one, according to Napoleon.org).

I found many explanations online, such as “he didn't trust anyone and liked to keep
his hand on his wallet” and “painters at the time charged by the limb.” But experts on Napoleon Series site’s FAQ say that the hand-in-jacket pose was “a common stance for men of breeding” and appears frequently in 18th-century portraiture. Even some ancient Greek and Roman statues have hands in togas.

Napoleon probably didn’t actually sit for the painting; an admirer commissioned that work and the artist painted it from memory.

After consulting historians about the hand-in-jacket pose, author David Feldman writes that certain gestures were indeed part of photographers’ standard poses. For example, you’ll often see two men posed shaking hands or with hands on each others’ shoulders, meant to convey a friendship or familial relationship. Holding a Bible and pointing off-camera are other standard poses.

The historians also suggest that putting a hand in a jacket, or on a
table or other object, also might’ve been a way of keeping the hand
still for long sitting times.